Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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895 FXUS62 KRAH 261430 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1030 AM EDT MON SEP 26 2016 .SYNOPSIS... A quasi-stationary front across southwestern NC will return north as a warm front today as a cold front approaches from the west. The cold front will move very slowly southeast through the area Tuesday and into Wednesday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1030 AM Monday High pressure off the New England coast extends into east-central NC this morning, with an east-southeasterly flow banking moisture up against the mountains and ceilings varying from below 1000ft in the west to 3000-4000 ft in the east. Persistent convection around the Charlotte Metro area has shown signs of waning in the past couple of hours, likely owing to a relaxation of the nocturnal LLJ and weaker isentropic accent. This precip, along with addition showers expected to trigger within an instability axis running up the foothills this afternoon, will have less moisture and forcing to work with as the mid-level flow carries it eastward. Thus, we will run with POPs varying from 30-40% in the western Piedmont to 20% near US-1. Temperatures continue to be a tough call, especially in the western Piedmont, as a southeasterly wind has developed, but the moisture (stratus) is somewhat trapped horizontally but the mountains and vertically by a weak CAD-like inversion (per 12z GSO raob). However, 850/925mb temps are around 16-18C over the southern and western portions of the Piedmont, so the airmass will support strong warming if/when clouds breaks. We`ve blended in some HRRR and LAMP guidance to help with the uncertainty and possible gradient, which yields mid 70s northeast to mid 80s southeast. Tonight: Sfc cold front is forecast to slip east of the mountains, but remain west of the forecast area through daybreak Tuesday. Upper support is almost non-existent, so expect convection to be tied closed to the low-level moisture convergence along the front and thus expect bulk of shower activity to remain across the NC Foothills and Western Piedmont. Lows in the mid 60s to lower 70s.
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&& .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 415 AM Monday... Low-level frontal zone stretched across central NC will slow down, potentially temporary stall across the area as the closed upper low over the Great Lakes and attendant deep upper trough begins to digs south into the Ohio Valley and southern Appalachians. Axis of 1.6- 1.7" PWAT attendant to the front will be centered across the area Tuesday afternoon and Tuesday night with numerous showers and scattered thunderstorms expected to move slowly south-southeastward across the area. Weak mid-level lapse rates should again limit destabilization and thwart severe threat. We could however see some locally heavy rain and minor flooding with models suggesting rainfall amounts widespread rainfall amounts of a half inch to an inch, with locally higher amounts of 1 to 1.5 inches possible. The front should settle slowly across eastern portions by late Tuesday evening/night with rain chances beginning to taper off from nw to se by daybreak Wednesday. Highs in the mid 70s northwest to lower 80s se. Lows Tuesday night 60 to 67. && .LONG TERM /Wednesday through Sunday/... As of 345 AM Monday... Forecast confidence remains below average due to an atypically complex synoptic pattern expected to evolve over North America mid/late week. The 00Z GFS/ECMWF both indicate that an upper level low amplifying over the Great Lakes early this week will dig southward through the OH valley and cut-off in vicinity of the TN Valley/Mid-Atlantic through mid/late week as an expansive upper level ridge builds over the eastern 2/3 of North America, though disagreement persists w/regard to the precise evolution of the cut- off low. Broadly speaking, long range guidance supports above normal chances for cloud cover/precipitation and slightly below normal temperatures mid/late week, though further details (i.e. precip amount/timing and perhaps severe wx potential) remain difficult to ascertain at this time. -Vincent && .AVIATION /12Z MONDAY THROUGH THURSDAY/... As of 740 AM Monday... Southerly moist upglide atop a quasi-stationary frontal boundary that extends across the western piedmont will support a chance of showers primarily over the western and central piedmont this morning. The front will retreat northeastward as a warm front between 15 to 21z. IFR to MVFR ceilings over the piedmont will lift to VFR with the passage of the warm front. Moisture pooling ahead of a cold front moving into the mountains will also support a small chance of showers and possibly a thunderstorm late in the afternoon/early evening with rain chances increasing overnight with sub-VFR ceilings as the front approaches the NW Piedmont. Looking beyond the 24 TAF Period: A cold front will move very slowly se through the area Tuesday and into the day on Wednesday. Showers and storms with associated periods of sub-VFR conditions are expected to accompany the front. Conditions are expected to improve to VFR from northwest to southeast Wednesday-Wednesday night as drier air filters into the area. During midweek, a rather unsettled pattern is expected to evolve as a deep upper low sags southward from the Great Lakes into the Central Appalachians. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL/BS SHORT TERM...CBL LONG TERM...Vincent AVIATION...CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.